Some of the games mentioned are actually very good games (Friday the 13th for NES), while others are widely misunderstood (Bokosuka Wars, which is perfectly decent for what it is & when it was released).

Pac-Man is a bad port but a perfectly playable game, and Tomcat Alley is one of the better FMV games on Sega CD -- you should try Supreme Warrior or Slam City if you want to see how low the FMV library could sink.

I also like Plumbers Don't Wear Ties, inasmuch as it's funny as hell. It may be a bad "game" -- really, more of a visual novel -- but I got more entertainment out of it than plenty of "good" games.

Anyway, what's the worst game I own? Probably some PlayStation shovelware I haven't even tried yet, or one of the RCA Studio II games my wife inherited from her dad (no console). But as for games I've actually played, I'd nominate:

Hockey/Soccer (Odyssey^2) < though I sold it; truly terrible game though
Andre Agassi Tennis (Genesis)
Onslaught (Genesis)
Fist of the North Star (Game Boy)
Race Drivin' (SNES)
Shadow: War of Succession (3DO)

I'm sure there are others worth nominating, but these stand out. Shadow: War of Succession is especially horrendous -- it's a would-be Mortal Kombat clone that looks, sounds, and plays like a damaged Flash game ca. 1999. As for Onslaught, it's barely even a game.